/Engine/Source/Runtime/HeadMountedDisplay/Public/IHeadMountedDisplay.h
Optional method to draw a view's visible area mesh where supported. This can be used instead of a full screen quad to avoid rendering pixels which are not included as input into the final distortion pass.
virtual void DrawVisibleAreaMesh ( class [FRHICommandList](API\Runtime\RHI\FRHICommandList) & RHICmdList, int32 ViewIndex ) const